Dark sky on Sunday: three focal lengths

 I was so excited by last-night's results that I posted them first.  However, the previous night (Sunday, 10 May) was almost as dark.  On Sunday I measured sqml=21.78 mpsas directly overhead.  The linear brightness ratio between 21.84 and 21.78 is 1.06.  Less than ten-percent differences are generally below the level of perception.

On Sunday I used three lenses:  Rokinon 7.5mm f/3.5 fisheye, Leica 25mm f/1.7, and the Olympus 75mm f/1.7.

 

Venus setting over Bristol Head.  Rokinon 7.5mm fisheye.

Jupiter setting over Bristol Head. Rokinon 7.5mm fisheye.

In the above image I applied a 3x3 Median filter to suppress the myriad of faint stars and emphasize the sky-brightness gradations caused by airglow and Zodiacal Light.  A faint arc of Zodiacal Light stretches up to the left from Jupiter in the lower middle of the frame.

Looking north.  Rokinon 7.5mm fisheye.

 In this image, the Big Dipper is in the middle of the frame.  An arc of Zodical Light curves up along the left edge.  In the bottom right corner the northern Milky Way is emerging above the NE horizon.  A median filter was also applied to this image.

Melotte 111. Leica 25mm f/1.7 + softon filter.

 The star cluster known as Melotte 111 (Mel 111) is the centerpiece of the constellation Coma Berenices.  The cluster was almost directly overhead.

Omega Centauri. Olympus 75mm.

 The giant globular cluster Omega Centauri clears the distant summit of Piedra Peak by only 1.8 deg.

Late-Night Wonders under a 21.84 sky

The measured sky brightness directly overhead last night was an astounding 21.84 mpsas.  This continues a several-day trend of some of the darkest skies I have seen in Creede for quite a while.  The sky becomes brighter toward the horizon because of airglow, a natural phenomenon in the upper atmosphere.  This low-elevation brightness is evident in the following image of Omega Centauri. 

 Omega Centauri is the largest globular cluster in our galaxy, containing approximately 10 million stars.  May is the best month for viewing this cluster from Creede.  Near midnight it skims along the southern horizon just above the peaks of distant mountains.

All of the images in this post were taken with an Olympus E-M1iii camera and Olympus 75mm f/1.8 lens.  Exposures were generally 60 sec at ISO 1600.

looking south toward Omega Centauri and Centaurus A

 In this image, Omega Centauri is about to pass (about 10 minutes later) 1.8 deg over the top of Piedra Peak.  Directly above it near the top of the image is the fainter galaxy NGC 5128, otherwise known as Centaurus A.  Airglow gives the sky a faint green coloration.

Omega Centauri

 

Centaurus-A, NGC 5128

Just before midnight, Scorpius and its brightest star Antares are rising above the ridgeline of Snowshoe Mountain:

Antares, M4, and the Rho-Ophiuchi Nebula

Rho Ophiuchi is the star at the center of this image, surrounded by blue nebulosity. This region consists of many bright and dark nebulae and is known as the Rho Ophiuchi cloud complex.

 To the west, the bright "Beehive Cluster" (M44) and fainter nearby cluster M67 are sinking toward the Bristol Head ridgeline:

M67 (left) and M44 (right)

 

M67

M44

The dwarf galaxy Leo I lies only 12 arcminutes from Regulus, the brightest star in the Constellation Leo and the 21st brightest star.  This galaxy was discovered in 1950 with the 48-inch Schmidt camera at Palomar Observatory.  Today it is possible to image this galaxy with a 42-mm aperture camera lens in a 60-sec exposure under suitably dark skies.  Technology has come a long way in 76 years.  

For a sense of scale, 12 arcminutes is the same as the separation between Mizar and Alcor, the famous naked-eye double star in the handle of the Big Dipper. 

Regulus (center) and Leo I (faint blob up and to the right)

 The galaxy Leo I is believed to be the most distant satellite galaxy of our Milky Way, at a distance of 820 kly.  Regulus is 79 ly distant, so this background galaxy is more than 10,000 times farther away.

The darkest sky with a fisheye lens

I was wanting to try out some night-sky photography with a fisheye lens, but the early evening was very cloudy and not very promising.  However, when I looked outside around 11:30 pm it appeared to be clear.  I assembled an Olympus E-M5iii with a Rokinon 7.5mm f/3.5 fisheye lens and put it on a tracking mount and got set up in the back yard.

The sky was indeed clear, although I could detect some murk along the north and south horizons.  The measured sky brightness directly overhead  was sqml=21.80 mpsas.  I was shocked.  The darkest sky anywhere generally tops out near 22 mpsas, so this is nearly as good as it gets.  I have measured a darker sky here in Creede only once.

Composition with a fisheye lens is tricky.  If the lens is tilted upward, the horizon will curve up on each side as it is in this image:

Rokinon 7.5mm f/3.5, ISO 3200, 60 s.

 This image was processed from the raw data to bring out the faintest details of airglow along the horizon.  The zenith point, where the sky is darkest, is about 1/8 of the frame down from the top.  The sky can never be truly black because of air glow, which is a natural high-altitude phenomenon caused by the sun.  Most of the time it is imperceptible to the eye, but easily picked up by long exposures with a camera.

The constellation Scorpius and its brightest star Antares was just emerging through the murky airglow above Snowshoe Mountain:

 Higher in the sky, a meteor was captured between Corona Borealis and Arcturus:

 

The ISS was the opening act

 Last night during Nautical Twilight (about 8:40 pm MDT) the International Space Station (ISS) made a highly visible pass over Creede, moving from SE to NE.  The sky was too bright for a long exposure, but I was able to capture it with a few short exposures.  

 

ISS over Snowshoe Mountain.  1.3-sec exposure.

About 30 minutes later Jupiter and Venus were shining brightly over the Bristol Head ridgeline during the onset of astronomical twilight.

Lens: Lumix 20mm f/1.7 + Hoya Sparkle-6 filter

 After Venus set, Jupiter was the brightest object in the sky:

Lumix 20mm + Sparkle-6 filter

 

Leica Summilux 25mm f/1.4 + softon filter

In this image, Pollux and Castor are to the right above Jupiter,  Procyon is to the lower left, and the "Beehive Cluster" (M44) is at the top of the frame.

 

Auriga setting over Bristol Head.  Lumix 20mm + sparkle filter

Corona Borealis.  Leica 25mm + softon filter

In this image of the constellation Corona Borealis, the dotted circle marks the location of the recurrent nova T CrB.  This star is currently at magnitude 10.1, but when (or if) it erupts again, it is expected to increase in brightness by a factor of a thousand, or more.  Of course, as the SEC warns, "past performance does not guarantee future results". 

The measured sky brightness at the conclusion of this outing (about 10 pm) was 21.62 mpsas, a very good (meaning very dark) value. 

Twilight planets

 These images were taken just after 9 pm MDT, at the end of Nautical Twilight.  The camera was an Olympus E-M1iii + Olympus 12mm f/2 lens with Hoya Softon and Sparkle-6 filters.  I was hoping for more photography later with a dark sky, but the clouds did not cooperate.

Venus at magnitude -3.9 is low over the Bristol Head ridgeline.  Jupiter is higher in the sky, shining at magnitude -2.0.  Above and to the right of Venus is the constellation Auriga and its brightest star Capella.

Softon filter

 

Sparkle-6 filter

Welcome Darkness

 Wednesday began with cloudy skies and snow flurries.  However, that changed, and while walking home late at night I was impressed by how clear and dark the sky was.  The sky brightness was measured as 21.65 mpsas, which is excellent for this area.  It helps that it is early in the season and a lot of the neighborhood cabins are dark and silent, with no windows or porch lights blazing.

These images were taken with an Olympus E-M1iii camera and an Olympus 12mm f/2 lens and a Hoya Softon filter.  Unfortunately, the focus was slightly off, but that is mostly hidden by the size reduction employed for these versions of the images.

 The three brightest objects in this image are, from left to right, Procyon, Jupiter, and Capella. Procyon is the eighth brightest star and Capella is the sixth brightest.  Just above Jupiter are the Gemini twins Pollux and Castor.  Castor (the right most) is a fine double star for small telescopes. There is just a blush of Zodiacal Light visible above the Bristol Head ridgeline and a hint of green airglow.

In the northerly direction the Big Dipper and Little Dipper are both standing high at this time of year.  The North Star, Polaris, is at the tip of the Little Dipper's handle.  Polaris is the nearest Cepheid variable, a class of stars important for establishing the cosmic distance scale.

 Looking toward the east, Arcturus is high in the sky.  Arcturus is the fourth brightest star and the brightest in the northern celestial hemisphere.  Below and left of Arcturus is the constellation Corona Borealis, outlined by a box in this image.  This constellation is being closely watched for the expected reappearance of a recurrent nova, T Coronae Borealis.  This nova is believed to erupt every 80 years.  The last eruption was in 1946.

 

Wintry welcome

My first day back in Creede was windy with snow flurries.  I was surprised to see stars when I looked outside just before 8 pm.  This shot of Venus hanging low over the Bristol Head ridgeline was obtained with a Sony A7III camera and a Rokinon 75mm f/1.8 lens.